I haven't seen the picture but it's very likely that it came from Republic, because Northwest bought Republic in the middle of the 1980's. Republic had a few 757's. Remember?
If you look closely at the engines, they should be Rolls Royce.

I just looked at the photo. It is N603RC, an RB211 powered ex-Republic 757-2S7. The aircraft was operated for a while in that hybrid scheme. The aircraft currently flies as N903AW with America West. It is msn23323, and was the 80th 757 off of the line, built in 1985. NW operated it from the time of the merger until June 1987, when it was returned to Boeing Capital Corp., and then passed on to the new lesee, HP.